322 SEX IN MICROORGANISMS 



varieties in Euplotes patella and two more sexually isolated varieties 

 in a morphologically distinct but similar form. Mating types occur 

 within all these varieties, but only one of. the E. patella varieties has 

 been studied in detail. In this variety six "mating types" are reported. 

 When animals (with some culture fluid) of one type are mixed with 

 animals (and fluid) of any one of the other five types, conjugation 

 occurs in the mixture. The course of events in such mixtures differs 

 in three ways from what has been described for Faraviecium: (1) 

 no sex reaction of any kind occurs for at least 90 minutes (Kimball, 

 1939); (2) mass mating reactions never occur; and (3) animal-free 

 fluids induce conjugation (selfing) in at least some of the other types. 

 The later events in conjugating Euplotes approximate the usual ciliate 

 pattern (Turner, 1930; Kimball, 1941; Katashima, 1952) and need 

 not be considered further, but the three points mentioned above de- 

 part radically from the scheme devised for Faraviechnu and warrant 

 serious treatment. 



Since the action of culture fluids is the striking feature in Eu- 

 plotes, this subject will receive primary consideration. Three conju- 

 gation-inducing agents are found among the six mating types. Ani- 

 mals may produce one or two of these, depending upon their genetic 

 constitution (Kimball, 1942). The production of the substances de- 

 pends upon three allelic genes, one aflele for each substance. There 

 are, then, six kinds of animals (the six mating types), three which 

 produce one kind of substance (homozygous animals) and three 



TABLE \T 



Conjugation-Inducing Action of Animal-Free Culture Fluids 

 IN Euplotes patella 



Conjugation ("selfing") is indicated by +; failure to observe conjugation by — . 



